laissez les bon temps rouler

A recent Advocate story by John Simerman provided an overview of how hotter weather does not produce more shootings in New Orleans. This Behind the Numbers post aims to complement that piece by providing the numbers and graphs behind the story.

There’s a common refrain in New Orleans that when summer arrives there is an accompanying increase in gun violence. This sentiment is captured in the video below.

This 2009 WDSU report notes that police call summer their “busiest time of year.” It is punctuated by a senior NOPD officer saying police “traditionally see an increase (in gun violence) in the summer months just because everybody’s outside” at around the 0:56 mark of the video.

The idea that gun violence rises in New Orleans in the summer has been around forever, and it persists today, as shown by this article from February 2015. That story cites various local experts who say that “during the winter and bitter cold weather, crime goes down, and in the summer it tends to go up, which is why the current murder rate is even more alarming.”

The idea that shootings and murder go up over the summer months is perfect to analyze because it is an answerable issue needing only publicly available data. The resulting analysis largely disproves the myth that there are more shootings during New Orleans’ hotter weather.

The first step in this analysis is to combine shooting data for each day since January 2011 with weather data for each day over that frame. How to compile the shooting data was described in this post, and the weather data can be found on Weather Underground.

The result is a spreadsheet with each day from January 2011 through June 2015 with the number of shooting incidents (total and fatal) in one column and the high temperature for each day in another. From there a record of how many shootings took place at each individual degree of temperature and how often the city had a high of each degree since 2011 can be created. The final step is to create scatter plots using the number of shootings (total and fatal) per temperature occurrence. The result is provided below.

Shooting incidents in New Orleans by temperature, 2011 – June 2015. Source: NOPD and Weather Underground.

The scatter plot of all shooting incidents (above) suggests there is virtually no relationship between the outside temperature and the number of shootings. The same is true of the scatter graph of fatal shooting incidents per temperature occurrence (below).

Just to be safe, one can run a regression analysis comparing shootings per temperature occurrence and the high temperatures to confirm the lack of a relationship. A regression analysis of total shooting incidents produces an R-squared of .04.

While the summer months may not produce more gun violence in New Orleans, it is certainly plausible for the summer to be more violent in other locales (and I will have a future post showing this to be the case in a Northern city).

A very interesting Governing.org report reviewed UCR data for 384 “larger law enforcement agencies” for evidence of summer crime surges. That report found that “areas where crime surges the most in the summer tend to be northern cities in states like Minnesota and New York.” Governing.org reported that “a few of the law enforcement agencies that registered the steepest fluctuations in crime serve summer tourist destinations.”

Of course, New Orleans is neither a northern city nor is it a summer tourist destination, so a lack of a summer bump in violent crime aligns with this report.

This relatively quick analysis shows that while temperatures may go up over the summer months, the likelihood of a shooting on any given day does not.